If you try to start a new rectangle on the edge of an existing rectangle, it deletes the existing one.
You can end on an existing rectangle, or just leave them free floating. Which is really confusing me.

I had issues where if I just changed the side, I would start getting several rectangles. This would only be noticable if I dragged really fast and then let go.
And on the Stop section, it creates a rectangle with no tags.